Electrolytic production of aluminum



Patented Apr. 2l, 1925.

UNITED STATES PATENT OFFICE.

WILLIAM HOOPES, F PITTSBURGH, AND FRANCIS C. PRABY AND JUNIUS D. ED-

WARDS, 0F OAXIONT, PENNSYLVANIA, ASSIGNOBB T0 ALUHINUH COMPANY 0FAMERICA, 0F PITTSBURGH, PENNSYLVANIA, A CORPORATION 0F PENNSYLVANIA.

ELECTRLYTIG PRODUCTION 0F ALUMINUI.

Application llled December 21, 1922. Serial No. 606,284.`

To all whwn it may concern:

Be it known that we, IVILLIAM Heeres, FRANCIS C. FRARY, and J UNlUs D.EDWARDS, all citizens of the United States of America,

5 the said VILLIAM Hoorns residing at Pittsburgh and the said F aimaisC. Fiumi' aud JUNiUs D. EDwAims residing at Oakmont, all in the countyof Allegheny and State of Pennsylvania., have invented certain new anduseful Improvements in Electrolytic Production of Aluminum, of which thefollowing is a full, clear, and exact descri tion.

This invention relates to the production of aluminum of substantiallyany desired high degree of purity, by the electrolytic refining ofimpure aluminum or aluminum-alloys colptaining other substances. Severalmethoi s for the purpose have been suggested in the past, but it is wellknown that none heretol'ore proposed has been capable of conimercialoperation. In fact it has been widely held among those skilled in theproduction of aluminum that such processes are inherently impractical.Our invention is the result of ,extensive investigation und study of theproblems involved, combined with prac-tical work on a large scale, andhas been found to be thoroughly feasible. 'ith it we have produced'commercially, at

low cost, metal having a metallic aluminum content as high as 99.98 percent.

In our method impure aluminum or aluminum alloy is used in a. moltenstate as anode, iu contact with a superimposed bath or elec- .ti-olyte,preferably consistin of or containing one or more fused fluori s, withor without the addition of chlorids; the pure aluminum being depositedon a cathode of molten aluminum, preferably floating-on the bath l0 orelectrolyte. The invention embraces several advantageous features which,although capable of use separately, are especially ctlective whenemployed oonjointly. One of the most important of these is the provisionof an alloy, for use as anode, which at the operating temperature willbe sufficiently mobile to permit the aluminum contained in it tocontinually replace, at the surface of the anode alloy, aluminum removedthere- 5 from by the electrolysis. Without such provision impurities inthe alloy may be dissolved in the electrolyte and deposited at thecathode in such amount as te seriously affect the purit of the refinedmetal. Another feature o importance in our invention resides inpromoting the secondary reactions by which impurities diolved from theanode alloy are ria-precipitated thereon and those deposited on thecathode are re-dissolved in (the bath; as for example b producin anenergetic circulation where y the bath eely Washes, or is freely washedby, the wntiguous surfaces of the anode and cathode respectively. Afurther advantageous feature consists in maintaining at least a certainminimum proportion of aluminum in the anode alloy, as by withdrawnp,rmore or less of the latter and supplying fresh alloy in its place, forthe purpose' of preserving the selective aluminumdissolving action ofthe bath.

The electrolyte or bath which we prefer to employ in the present methodcontains aluminum iluorid, with the addition of one or more'fluorids ofmetals mori` electropositive than aluminum. Preferably the bath is ofabout the following composition:

ties, about 2 The addition of fluorids of other of the alkali oralkali-earth metals is permissible, but the presence of halogen anionsother than those of lluorin is undesirable, and indeed is highlyobjectionable if aluminum of a high degree of purity is to be obtained;0n the other hand, ther resence of oxygen anions is not usuallyobleetionable, and :iccordingly alumina may be an ingredient of thebath'. In some, cases alumina is a desirable ingredient, but not, ingeneral, in amount suicient 'to saturate the mixture. The use of a bathcontaining between 20 and per cent of barium luorid, or strontiumfluor-id in like amount, or a mixture of the two, is claimed broadly inour copendin application Serialv No. 608,285. Barium an strontium arealkali earth metals having atomic weights above 80.

Speaking generally, the bath or electrolyte A bath such as the above isfluid within the range of suitable working temperatures, and is of lowerdensity than the impure aluminum or aluminum allo `which has been foundin general most suitable for the process. Hence the bath will float onthe molten alloy. At the same time the bath is of higher density tla therefined or pure aluminum, so that the latter will float on the former.Moreover, the'bath described is capable of dissolving a substantialamount of alumina. For a more extended discussion of electrolytes forthe electrolytic relining of aluminum 'reference ma be had to thecopendin application -o William Hoopes and rancis Cs Frary, Serial No.608,286; and to our copendin ap lication, above mentioned, wherein t e eectrolytc preferred for our present invention is claimed broadly.

In general, any alloy of aluminum may be refined which has a greaterdensity than the bath or electrolyte and which will remainsatisfactorily mobile while the refining rocess is going on. In casethefdensit o the `alloy is too low it may be raised by t e addition of aheavier metal or metals. Of the metals that may be used for such urposecopper has been found preferable. n practice the working temperature ofthe preferred bath lies between 850 and 1,100" C., approximately, with apreferred temperature of about 950 (3. A bath of the above analysis hasat the preferred temperature lnentioned a density of between about V2.5and 2.7 grams per cc. Aluminum at the same temperature has a density ofabout 2.3 grams r cc. and, if it containsonly small quantities of heavymetals or even considerable uantities of silicon or other impurities olow density, will oat'- on instead of sinking in the bath. The presenceof about 25 r cent of copper gives an alloy mixture which at atemperature of 950 C. has a density of about 2.8. This is sulcientlyabove the density of the bath to insure that the alloy will not floatbut will remain at the bottom. A greater proportion of cop er may beused, however, provided the al oy is satisfactorily mobile at the ugperlimit of temperature for smooth wor ing, say between 1050 and 1100 C.-

The' freezin int of. pure copper 1s around 1083" hilt ,the addition of 2pery cent of silicon reduces the freezing point to about 1050 C., and analloy containin per cent of copper and 1B per cent of si icou num isextracted. 'Generally s ing point lowered from about 1050 C. to A about930 C. by the addition of 5 r cent of silicon, and to about 795". C. byt e addition of 10 per cent of silicon.. The presence of silicon inamount between 2 per cent and 32 per cent of the copper-plus-silicontherefore prevents the allo from freezing at a temperature of 1050 orhigher, and thus permits the removal of all or substantially -v all ofthe aluminum without causing the residual alloy to freeze at thetemperature mentioned. The presence of iron and titanium, or either ofthem, tends to raise the freezing point, which is 'of course, objactionable. t er materials than silicon will serve the purpose ofpreventing the freezing of the alloy as the aluminum is removed, but

silicon is preferred, and its cheapness permits it to be thrown awa slagwhen the residuaLal o `is afterwards treated for recovery of the copper.On the other hand, tin or other low-melting material miscible withaluminum and copper, would have to be thrown away, or would have to berecovered in the course of reclaiming the copper. In either case the netco'st of the process would be increased.

Aluminum has ofitself the capability of lowering the freezinpoint of coper, and Vadvantage may be ta en of this act, when necessary ordesirable, by removing the alloy from the cell while it still containssome aluminum. In other words, the amount of aluminum and the amount ofsilicon should be so adjusted with respect to the other constituentsthat the anode alloy will at all timesremain mobile within a rurrge ofworking temperatures which `will not cause ob]ec Vtionable alteration ofthe bath as by vola tilizal'ion of one or another of its ingredients.Thus if it is desired to remove all of the aluminum, the silicon contentwhen the aluminum has been removed should be not less than about 2 percent of the copperplus-silicon; but if the silicon content is not ofitself suflicient to maintain the desired mobility it may be necessaryto remove the alloy (or re lace a portion of it with fresh metal, oradld silicon) before all the alumiaking there ought to be enough siliconto ee the alloy mo ile at a temperature of 1000 or thereabouts, when thealuminum content has been `reduced to the desired extent. Silicon to theform ofY Ctl Athe upper electrodes to the amount of per cent of thecopper-plussilicon is ordinaril ample for the pur ose if the ironcontent is not more than a out 5 per cent. It is to be understood thatit is not in all cases necessary to have the alloy completely molten.Under some circumstances the presence of a limited amount of solidhigh-freezing material entrained in the anode alloy is not objectionableso lon as it does not reduce the mobility of the aglloy nough to preventits free circulation and For the above reasons, the anode alloy used ispreferably one containing copper in amount above per cent, and siliconin amount betwcen 2 and 32 per cent of the copperplussilicon,approximately. One of the applications of our invention is for therecovery of aluminum from electrothermally produced aluniinum-copperalloys, as for example one of about the following eimposition:

`Fer een' Aluminum Copper Silicon T 10 Iron, less than 5 Titanium, lessthan 1 A convenient and practical method for producing an anode-alloysuch as the above is described and claimed in our copending applicationSer. No. 608,283, filed December 2l. 1922.

In the refining operation, unidirectional or continuous current from anysuitable source is led into the anode alloy or impure aluminum andpasses ,upward therefrom through the bath or electrolyte to the cathodeabove, with resulting deposition of aluminum thereat. High enoughcurrent density is used to make the resistance losses within the cellsufficient to maintain the working temperature.

Convenient and suitable apparatus for practiciingY the present inventionis illustrated in the accompanying drawing, but it is to be understomlIliat the invention is not limited thereto. The apparatus illustrated isclaimed broadly in a copeiiding application of 'illiani Hoopes.

Referring to the drawing,

Fig. l is a plan view of the cell.

Figs. and 3 are cross sections on lines --2 and 3&3, respectively, ofFig. l.

lFigs. 4 and ."i are detail cross sectionson lines 4 4 and 5-5,respectively, of Fig. l, illustrating` the water loiinections to andfrom and between the water jackets.

Fig. ti is a detail cross section on line 6 6 of Fig. l., showing themethod of connecting the negative bushars.

Fig 7 is a detail cross section on the same planear: Fig. 2,illustrating the method 0f securing the upper and lower shell sectionstogether to give adequate mechanical strength without connecting the twoelectricaly.

Fig. 8 is a detail sectional view illustrating a suitable anode for usein deoxidizing the electrolyte. Fig. 9 is a detail section on the sameplane as Fig. 2, showing the heat-insulating top-- crust above thecathode metal.

The lower shell or shell section 10 is preferably made of steel in theforni of a cylindrical vessel of considerably greater dialneter thanheight, and at or near its top it is provided with a water` jacket 11which is inost conveniently formed by providing at the upper edge of theshell section an outwardly extending flange 12 of suitable width, and aflaring or conical ring 12 welded or otherwise hernictically joined tothe underside of the llange and to the body of the shell below.

Above the lower shell section l() is an up` per shell section 13 whichmay also be of steel and formed with hollow walls to provide an upperwater jacket 14. 'llie inner surface of thel upper shell section is|irefcrably flaring, as indicated. 'lo keep the sections electricallyinsulated or separated from each other a flat ringpr gasket 15, ofashestos or other suitable material, may be used between the two.

In order to give the shell structurisullicient mechanical strength .thesections may be secured together h incaiis of niacliinc studs 16 passingupwar ly through the flange 1L. and threaded into pads 17 welded on thcbottom of the upper shell inside the water jacket. 'Io preventelectrical connection thiI holes in the flange 12, through which thcstuds pass, may have insulating bushings 1H and insulating washers lt)may be used. -lf the water jackets are used, as in most-cases they willhe` the bushings and washers will not bc subjected to a high temperatureand hence they can be inade of practically :in v insulating materialwhich will not soften at temperatures below 100 C and which can witlistand the crushing stress exerted by tln` studs. Mica lnis been foundsuitable for the purpose.

Suitable water connections for thc water jackets are provided, and forthe sake ol' simplicity and convenience these connections may be soconstructed and arrang d that thc water flows through the two jackets insuccession, preferably through the lower jacket lirst. ,For this purposethc. jacket 11 may be provided at the bottoni with an inlet nipple 20connected b v a pipe 2l to any convenient source of water, not shown,and at the top (to prevent pocketing of air) with an outlet nipple 29.connected by a pipe lit to the inlet nipple 24 by which water from thelower jacket is lcd into the bfittoni ol' thc upper. The latter isequipped with :in outllt) let nipple 25 (at the top to prevent airpocketing) which may be connected to a waste pipe 26 by means of a pipe27. To avoid electrical groundi the pipes 21 and 2 `mayyconsist ofrubber ose, as may also tliepipe 23 to keep the two shell sectionselectrically separate. The water used when the jackets are connectedshould be of suicient purity to prevent the tlow of a substantial amountof current from one shell section to the other at the voltage employedin operation.

In the bottom of the lower shell section a layer 28 of heat-insulatingmaterial may be provided, as owdered bauxite, alumina, magnesia, or reractory'bricks, to decrease or minimize loss of heat through the bottomof the cell, and above this layer is a bottom lining 29 of refractoryelectrically conducting material, preferably carbon, and preferablyhaving a cavity or depression in its upper por ion to receive the alloyor other material to be refined. The bottom lining can be convenientlyand satisfactorily made by tamping into the shell a mixture of tar,pitch and` granular or powdered coke, at a temperature high enough tomake the mass plastic, and placingx the shell and contents in an oven inwhic the temperature is gradually raised, say to about 600 C., forthepurpose of baking and solidifyin the carbonaceous mass.

ood electrical connection may be provided between the shell and itsbottom linii by means of metal, collector plates 3l, weld to the innersurface-of the shell so as to be electrically and kmechanicallycontinuous therewith. These plates extend inwardly into the bottomlining, which is molded around them. At theplane of the 'collectorplates the shell may be provided on the outside with metal contact pads32, preferably welded to the shell so as to be mechanically andelectrically continuous therewith, to which pads busses or busbars, ofcopper, aluminum or other suitable metal may be bolted tightly in place.The busbars may be in the form of long flat plates 33 embracing thelower shell section, with their ends brought out at one side of thc cellfor convenient connection to one terminal of a suitable source (notshown) of continuous or unidirectional current. uring the refiningoperation these busses are connected to the^ positive terminal or pole4of the sour-censo that the current enters the cell at the bottom. Thecarbon bottom 4or bottom-lining, 29, constitutes what may forconvenience termed the lower electrode of the cell.

The upper electrode may. be multi le, com sed preferably of a suitablenum r of s ort thick rods or cylinders 34 of graphite, arrangedvertically and having co per or .other metal rods 35 threaded or oterwise suitably secured to the tops of the elecbe Horstie Yon t trodes.These metal rods serve to support the graphite cylinders and conveycurrent to or from the same, and for this purpose they may be releasablyand adjustably sesured, as by means of clamps 36, to metal busbars 37extending horizontally across the cell. For convenience of access to theelectrodes, for adjustment, re lacement, ete., the busbars may bearrange at two or more diiferent levels, as in icated, and may besupported on and secured to a plurality of legs 38 to form a rigidframework. The latter may rest on the u er shell section, in which caseit is preferable to have them insulated from the shell section, as byany convenient and suitable means, not shown.

It is recognized that, strictl speaking, the aluminum layer floati on te bath and the layer of alloy underlying the bath, are the upper andlower electrodes, respectively, but these layers are termed herein thecathode' and the anode and hence it is deemed permissible as w l asconvenient to refer to the graphite cylinders and the carbonbottom-lining, or their equivalents, as

the upper and lower electrodes.

Metal or other molten material ma be withdrawn from the/upper portion othe cell through a tapping notch 39 which may be closed b means of anysuitable refracto material w Aich will not contaminate the ce l contentswith which it comes in contact. Molten metal or other material ma;I bewithdrawn from the lower part o the cell through a ortor tapping hole40, normally close by means of a plug of dense charcoal or othersuitable material.

On the inside' of the 45 ext/ending upwardly from ottom 29, over thejoint between the shell sections and well up toward or evenover the topof the upr shell section. This sidelining should thermally andelectrically insulating, to decrease or minimize the conduction of heatto the water'j ets as well as to prevent by-passing of current aroundany part of the cell contacts `undergoing clectrolytic treatment in there ing operation. The lining should also chemically uiiobjectionable,and refractpry enough to remain solid at the temperatures to which it issubjected in the electrolytic relining operation. To meet theseconditions a lininr composed of or formed from .a mixture o metalfluorids and alumina, as more fully explained in the ap lication ofWilliam Hoopes Juiiius D. dwa'rds and Basil T.

Y id, sei-iai No. 638,289, has been found hi hly satisfactory inpractice. k

n the refining process the aluminum alloy or mixture of aluminum andother substances lies in molten form at the bottom of the cell asindicated at 46. Float' g on this is a layer 47 of fused bath or eectrolyte, and

ie latter is a layer 48 of molten alumithe carbon b cell is aside-liningl the bath.

num, with the upper electrodes extending into it far enough to insuregood electrical contract, say an inch or two. The molten layers may beestablished in the cell in any convenient manner, as for example bypouring the previously fused materials into place, using for theoriginal aluminum layer the purest metal conveniently availableu Thebusbars 33 are connected to the positive terminal of the source ofelectrolyzingtunithe busbars 37 are directional) current, and

connected to the negative terminal of the same source. Any convenientand suitable means, not shown, may be employed to regulate the voltageand current supplied. Apparently the effect of the passage of thecurrent is to set free liuorin or oxygen anions, or both, in Contactwith the surface of the anode metal. The eti'ectof the liberation ofthese anions is to dissolve, from the anode alloy, aluminum and anyimpurity present in thealloy which is more electropositive than aluminumand to leave behind the im urities which are less electropositive. Any othe latter impurities which may be attacked by the anions tend to beimmediately re-precipitated by a secondary reaction .between thealuminum, with which they are 1n contact, and the tiuorids or oxids ofthese ess electropositive metals, with the result that only aluminum andimpurities which are more electropositive pass into solution in In theanode alloy described above there are no impurities which are moreelectro-positive than aluminum and practically only aluminum goes intosolution so long as the aluminum content remains relatively high and theaforesaid secondary reactions can occur freely.

lVith a bath containing sodium and barium luorids there is alsodeposited at the cathode, along with the aluminum, some barium and solnesodium, the amounts being dependent to some extent at least upon theIcurrent i in the bath, and the bath density used, and the quantitativecomposition of the bath. ,t has been found, however, that both bariumand sodium react, at the working temperature, with aluminum iuorid toproduce metallic aluminum and barium or sodium fluorid, as the case maybe. Consequently so longas there is a sufficiently high proportion ofaluminum fluorid can freely wash the bottom of the cathode metal layer,no barium is found in the lat-ter metal; but at the working temperaturesodium, which is nearly insoluble in aluminum, is Set free in gaseousform and small proportions of it escape before the secondary reactioncan completely redissolve all of it. Hence minuto traces of sodium areoften found in the cathode met al, and some sodium escapes into theheat-insulating crust maintained above the top metal. This quantity,however` is usually very small when the bat-h is kept iu the propercondition of fusionand is not allowed to become deficient 1n aluminumlluorid.

Leadin electrolyzing current to the anode an from the cathode in suchmanner that a magnetic field is produced in the cell, is considered tobe an advantageous feature. 'lhus in the apparatus illustrated thecurrents in the upper transverse horizontal busbars 37 and verticalelectrodes 34, and in the lower encircling horizontal busses 33 andtapering horizontal distributor or collector lates 31, reduce in thecell a powerful an` non-uniform magnetic field having both vertical andhorizontal components. On account of the relatively high specificresistance of the electrolyte, as compared with that of either the anodealloy or the. top metal layer, the current density throu hout thehorizontal cross section of the electrol te and hence at its upper andlower sur aces, is substantially uniform. Likewise, the current densityat tl1esurface of contact between the conducting bottom lining and theanode alloy (which latter has much better conductivity than the former)is substantially uniform, although the conducting plates or ribs in thebottom lining tend somewhat to concentrate the current. But inthe anodealloy the current flow may have horizontal as well as verticalcomponents, due in part to the concentrating effect of the aforesaidplates in the bottom lining, and, probably more especially, to thebowl-like receptacle in the bottom lining, whereby some of the currentcan flow between the anode alloy and the conducting side Walls of thereceptacle. These horizontal components of current- How in the alloy arelargelyl radial in direction. The interaction of the current flowing inthe anode alloy and the non-uniform magnetic field produced as explainedabove, causes the anode alloy (which, being molten, is in effectcomposed of movable conductors) to flow in various directions, andproduces a powerful circulation and mixing of the ulloy. The stirringthus produced is, we believe, an important factor in replenishing theactive surface of the anode alloy with aluminum fast enou rh to satisfythe anions set free thereat, ma :ing possible more extensive removal ofaluminum from the alloy or the use of a higher current density, or both,without depositing impurities at the cathode in such amount as toseriously affect its quality. Moreover, the interaction of currents andmagnetic field in the bath and in the cathode produces a like stirringeffect in these layers which is advantageous in promoting homogeneity ofcomposition and temperature and especially in preventing the bath frombeing impoverished of aluminum at the surface in contact with thecathode. 'lhc stirring etl'ect described also quate opportunity for thetions by which elements secondary reac- (other than alumiiiuni)deposited at the cathode are re-dissolved in the bath and by dissolvedfrom thereon.

which impurities the anode are re-precip'itated As the refiningoperation proceeds, aluminum dissolved out of the anode alloy isdeposited in molten form and when the desired has been deposited metalis removed anode metal is withdrawn hole 40, state` being supplied suchthat bath will not be tion ma means o ing preheated, is let bottom ofpreferably been cut out of refined metal entrappxed dl fte an a e,a.rwhic be di pcd out with a the resh anode metal is funnel is thenliftpd out.

contaminated. be conveniently a carbon funnel, w

down until the cell, which has on the cathode,

amount of aluminum a portion of the top and the impoverished thro h thetap fresh anode metal 'in t e molten in any convenient way, the refinedmetal oatin 0n the This operal rformed by ich, after beit nearly thecircuit. The the funnel may ou in. The ie fresh anode metal introducedis preferably sufficient in amount to raise the until the surface of theThe tapping bath and top metal latter is at the before the withdrawal.

out and replenishing operations may be re eatedfrom time to time asnecessary or interrupting the refining otherwise can Notwithstancapillary action at tween the liquid esirable without seriousl process,whic on continuously. ing the greater density of the bath, a portion ofit is carried up the area of contact aluminum and the so lid boundarycrust and rises to the surface of the former, where it s the weight ofwhich is come the surface tension of prends in a thin layer,

insufficient to overthe liquid alumiiium. Consequently it spreads overthe entire surface of the latter,

the escape of heat into the air,

a crust such there, forming for example, at 58, oii until the resultingcrust that (the escape of heat bein its un er surface can thetemperature of rise to the melting point this thickness saturated bathsubsequentl and b y reason of solidiies as is indicated,

Fig. 9. This process goes thickens so muc thus retarded) the bath. When'is attained, quantities of uny carried up by capillary action canaccumulate in liquid form under the crust and finally grow to a mass ofsufficient sink through the dimensions to aluminum.

be able to ence if the bath is kept unsaturated' with alumina the topafter which crust forms up to a certain thickness,

its growth ceases. On the other hand if the freezing point of the bathis raised by allowing it to become saturated, liquid bath finding itsway to the under-surface of the crust partially solidilies there andincreases the thickness. This action would, if unchecked, resulteventually iii bringing up a lar e portion of the bath from below thealuminum and causing it to attach itself to the top crust. At the sametime, the boundary crust at the sides of the cell thickens in the samemanner, and the net result would ultimately be more or less completesolidification of the bath unless its temperature is raisedcorrespondingly. For these reasons it is desirable to keep the bathunsaturated in the normal operation of refinhe bath crust formed on thealuminum layer as above described serves as a convenient and goed heatinsulating medium to minimize oss of heat from the top of the cell butit also entraps sodium as already explained, with consequent increase oalumina in the bath. The amount of sodium which thus escapes from thebath can be minimized by using in the latter the highest permissibleamount of aluminum fluorid.

Instead of forming the heat-insulating top crust in the manneriereinbefore specifically described, such a crust mayy be produced bydusting over the up er sur ace of the aluminum la er,-soon a er it isput in place, a layer o finely divided alumina, carbon, ma nesia, orother suitable wdered materia This layer of finely divi ed material israpidly cemented together by tlie liquid bath coming u from below andwetting it. The heat-insu ating property of the top crust may beincreased by dusting any suita le powdered material over it after it hasbeen formed, so that it is covered by a layer of such material, which isan excellent insulator by reason of its porous condition. Being su pliedto the surface of the to crust after t e latter has solidified, the aditional heat-insulating material is not cemented together and thereforeretains its porosity. In

eneral, the best material for the purpose is bath which has been allowedto soli ify, since if any of it accident ally or incidentally finds itsway below the top metal it does not contaminate the electrolyte.

Several methods are available for keeping the alumina content of thebath below the saturation point. For exam le, the to metal (aluminum)can be lad ed or tappe ortion of the saturated or nearly ath dipped out,liquid or solid alumina-free or deoxidized bath being added to take theplace of that which was removed. The resulting mixture will then be wellbelow the saturation point. 0r a portion of the crust can be broken awayand removed, whereupon it will reform at the expense of the saturatedbath within the cell,

4the excess alumina crystalliaing out in co- Hall process of i isillustrated in Figs. 1

rundum-like form. New alumina-free or deoxidized bath can be addedeither in solid or liquid form to take the place of that which went toform the new crust. In the first method the saturated bath removed fromthe cell can be regenerated and prepared for reentry into the process bycrushing it and electrol zing it.

Anot er method of preventing saturation of the bath with alumina is todeoxidize the alumina continuously, or from time to time, in therefining cell itself, for example by electrolyzing the bath according tothe producing aluminum from alumina. This may be accomplished by placinga carbon electrode in contact with the bath and connecting it with thepositive terminal of the cell, thus making the carbon electrodeV ananode. Any current vleaving this carbon anode serves to electro] zealumina in the usual manner, depositing aluminum on the cathode metal,or on the anode alloy, or on both, depending u on the voltage used; theoxygen being li erated at the carbon anode an forming CO2 with a portionof the carbon. The preferred way of using a carbon anode for the purposeand 8 of the drawings. p In these figures 50 represents a carbon diskinto which is threaded a carbon stud 51, into the up er end of which isthreaded a water-coo ed iron terminal 52. The latter is screwed into thebottom of a pipe 53 which serves to support the terminal and the diskand also to supply the electrolyzing current and the cooling Water. Atits top the pipe is fitted into the underside of a closed chamber 54through which a Water supply ipe 55 projects down into the pipe and welto the bottom of the latter. Water thus introduced into contact with theiron terminal 52 rises around the pipe 55 and flows out of the chamber54 by way of pipe 56. The pipe 53 is fastened on an insulated support 57in such manner as to hold the carbon disk 50 submerged in the bath belowthe aluminum layer 48. 'Around the carbon stud 51, water-cooled terminal52 and thelower end of pipe 53, is an insulating and refractory crust 58which may consist of a mixture of bath and corundum previously cast inplace. This crust serves to prevent the aluminum top metal from makingcontact with the carbon disk or with the electrically associated parts,and thereby prevents a short-circuit between the top metal and thedeoxidizing anode. The latter can be electrically connected with thepositive bus inauy convenient manner, preferabl through a suitablecircuit-breaker, not s own, from which current may be carried by meansof a cable 59 connected with the pipe 53. In practical operation it isusua ly sutlicient to deoxidize the bath intermittently, depending uponthe rate (as determined by experience) at which oxygen finds its wayinto the bath. n

The energy-eliiciency in electrolytic processes of refining aluminum isdependent largely upon the perfection of the measures taken forpreventing escape of heat. .'lheoretically a most no energy is requiredfor the refinin but practically, in the absence of some oter adequatesource of heat, suiiicient electrical energy must be expended tomaintain the anode, the bath, and the cathode, in a fused condition, andconsequently the amount of electrical energy which must be supplied isalmost exactly the equivalent of the heat )ermitted to escape. After theheat insu ation of the cell has been perfected to the maximumpracticable extent, nothing further can be accomplished in limitation oftheanlount of heat escaping iven dimensions, and with the minimumieat-loss the energ input required by the cell will also be a minimum.In the interests of power economy the cell should `be operated at thelowest practicable yoltage. Accordingly the electrolyte, which furnishesthe major portion of the resistance. should be in as tlnn a layer as ispermissible, and it has been found that a layer from 2.1/2 to 4 inchesthick is in general satisfactory. With a bath or electrolyte of anypredetermined workable depth, the current density permissible variesbetween af lower limit which is sufficient to maintain the anode, thebath and the cathode in afmolten state, and an upper limit at which"olatilization of the bath is excessive or at which too large aproportion of anode impurities go into solution. These limits. with thevarious bath-com ositions which have been found practicab e, areapproximately 800 (l. and 1100o C., respectively, with a preferableworking temperature of about 050 ("1. The permissible lower limit ofcurrent density also varies inversely with the dimensions of the cell,since the heut loss per unit ot' rolume in a large cell is lcss thanthat in u small cell on account of the smaller ratio of heat-dissipatingarea to the volume.

In a cell having a cross section through the electrolyte of 9.6 squarefeet it hasbecn found that the preferable current is, in general, 8500amperes, but that the process is workable with currents between 7500 and12000 amperes. The preferable current density in a cell having theelectrolyte crossvsectional area mentioned is therefore 885 amperes persquare foot, with a permissible minimum of about 780 ampere-s and apermissiblemaximum of about 1250 amperes, per square` foot. With thepreferred current density mentioned, the total voltage between theterminals of the cell may be about (i volts. Larger cells may beoperated with louter current densities and at lower voltfrom a heatedbody of,

llO

ages, and by varying the size of the cell, the composition of the bath,the conductivity of the bath, and the effectiveness of the heatinsulation, the present electrolytic refining process is workable Withcurrent densities between about 50() and about 2500 am eres per squarefoot of cross section of the ath. In general the lower practicable limitof voltage is about 3.5 volts and the upper limit is of courseindefinite.

rl`he layer of aluminum floating on the molten bath or electrolyteshould be of suiiicieiit expanse to touch the boundary crust ot the cellaround the entire perimeter thereof and should be thick enough to insurefirm contact with this crust, in order to prevent or minimizevolatilizatioii of the bath, which occurs to a great/er or less extentat working temperatures and increases as the temperature rises. Onaccount of the surface tension of liiolteii aluminum the top layershould be ot substantial depth, and it is therefore desirable tomaintain a thickness of at least 2, inches at all times.

So long as the aluminum content of the anode. alloy is not much below 10per cent, by weight, no ditliculty is ordinarily experienced inobtaining a cathode metal having a purity adeipiate for commercialrequirements. On tie other hand, as the anode alloy becomes impoverishedof aluminum the selective action ot the bath becomes more and moreimpaired, impurities in the anode are dissolved in larger amount, andmore and more of such im urities are deposited on the cathode. But yremoving impoverished alloy and substituting fresh whenever the aluminumcontent has fallen too loW the major portion of the latter metal can beobtained in very pure form. The impoverished alloy can be disposed of inany advantageous manner, but for the purpose of making the copperre-iiseable the alloy may be sent to a copper refining furnace Where themajor portion of'the remaining iron, titanium, and silicon may beremoved by the common method of oxidation and slagring. ()i,in casethese impurities are lovv, the alloy may be diluted with impurealuminum, such, for example, as is produced by the Hall process, andthen returned to t-he cell. It molten impure aluminum be convenientlyavailable, the impoverished alloy may be tapped into a criiciblecontaining the desire amount of molten aluminum, thoroughly stirred, andpromptly returned to the cell, so that the retiniiig operation pioreedswith the use of the saine copper.

It is to be understood that the invention is not limited to the specificprocedure and apparatus herein illustrated and described but can bepracticed in other ways without departure from its spirit.

lVe claiml. In the refining of aluminum, the steps composition of theallow comprising electrolyzin a molten bath with a molten allo as ano econtaining aluminum materiali;Y in excess of the amount required tomaintain the alloy mobile at a temperature too low to causeobjectionable alteration of the bath, and depositing said excessaluminum in the molten state on a molten aluminum cathode in contactwith said bath.

2. In the refining of aluminum, the steps comprising electrolyzin amolten bath with a molten aluminum a loy as anode compounded to remainmobile below a temperature causing material alteration of the bath, anddepositing iii the molten state on a molten aluminum cathode in contactwith said bath, aluminum removed electrolytically from the anode.

3. In the refining of aluminum, the steps comprising electrolyzing amolten bath with a molten aluminum alloy as anode containing siliconproportioned to cause said alloy to remain mobile below a temperaturecausing material alteration of the bath, and depositing in a moltenstate on a molten aluminum cathode the aluminum removed from said allo4. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten aluminum alloy as anode containingsilicon in amount adapted to maintain the allo in a mobile stateregardless of its diminis iingaluminum content, and depositing theremoved aluminum on a molten aluminum cathode through a molten bath.

5. In the refining of aluminum, the steps comprisin removing aluminumelectrolytically rom a molten aluminum alloy as anode and depositing thealuminum upon a molten aluminum cathode through a molten bath, andcontrolling the bath and anode compositions to provide a common lowtemperature of mobility and maintain a definite relation of theirdensities.

6. In the refining of aluminum, the steps comprising electrolyzin amolten bath with a molten aluminum a loy as anode compounded to remainmobile below a tem rature causing material alteration of the girth,depositing said excess aluminum in the molten state on a molten aluminumcathode in contact with said bath, and correcting the from time to timeto maintain its mobility.

7. In the refining of aluminum, the steps comprising electrolyticallyremoving aluminum from a molten alloy thereof having a com ositionenabling the alloy to remainmobile at the operating temperature anddepositing the aluminum on a molten aluminum cathode tlirou h a moltenbath capable of acting selective to dissolve aluminum from the alloy,andyby Withdrawal and replenishment of the alloy as it becomes im- HtlAIl() poverished maintaining an alloy composition adapted to preservesaid selective action of the bath.

8. In the iefining of aluminum, the steps comprising electrolyticallyremoving aluminumfrom a molten alloy thereof and deacting selectively todissolve aluminum from the alloy, and maintaining the aluminum contentof the alloy high enough to preserve said selective action of the bath.

9. In the refining of aluminum, the steps comprising electrolyticallyremoving aluminum from a molten alloy thereof containing copper andsilicon in proportions adapted to keep the alloy mobile during theelectrolysis and depositing the aluminum on a molten aluminum cathodethrough a molten bath capable of acting selectively to dissolve aluminumfrom the alloy, and b Withdrawal and replenishment of the al oy as itbecomes impoverished maintaining an alloy composition adapted topreserve said selective action.

10. In the refilling of aluminum, the steps comprising electrolyticallyremoving aluminum from a molten alloy thereof containing copper andsilicon in proportions adapted to keep the alloy mobile during the.electrolysis and depositing the aluminum on a molten aluminum cathodethrough a molten bath capable of acting selectively to dissolve aluminumfrom the alloy, while maintaining the aluminum content of the alloy highenough to preserve said selective action of the bath and maintaining a.current density and circulation of the bath, with respect to thecontiguous anode surface, adapted to permit at said surface secondaryreactions ade nate to prevent permanent solution of anode impurities inthe electrol e.

11. In the refining of aluminum, the steps comprising electrolyticallyremoving aluminum from a molten alloy thereof containing copper andsilicnn in proportions adapted to keep the alloy mobile during theelectrolysis and depositingr the aluminum on a molten aluminum cathodethrough a molten bath capable of acting selectivel to dissolve aluminumfrom the alloy; whi e maintaining an alloy composition, and a currentdensity and circulation of the bath, with respect to the anode andcathode surfaces, adapted to permit at said surfaces secondary reactionsadequate to precipitate, on the anode, impurities removed therefrom, andto revent permanent deposition `onthe cat ode, of bath components moreelectropositive than aluminum.

12. In the refining of aluminum, the steps comprising electrolyticallyremoving aluminum from a molten alloy thereof as anode and depositin thealuminum on a molten aluminum catiode through a molten bath a molten'main mobile,

capable of ,acting .selectively to dissolve aluminum from the alloy,while maintaining bath and alloy compositions, and an anodecurrent-density and circulation, adapted to minimize removal of metalsmore electroncgative than aluminum from the allo and causeprecipitation, on the alloy, o said more electronegative metals.

13. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from molten alloy thereof as anode and depositing thealuminum on a molten aluminum cathode through a suitable molten bath,and giving free plav to secondary reactions at the active sur aces ofthe anode and cathode, by maintaining intimate contact between the bathand the anode and cathode, maintaining active circulation of the bathand anode, and controlling the composition of the bath and anode and thecurrent densities at the active surfaces thereof.

14. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten alloy thereof as anode and depositing thealuminum on a. `molten aluminum cathode through a suitableI molten bath,said anode alloy having a composition enabling-it to remain mobile belowa temperature causing material volatilization of the bath; and givingfree pla to secondary reactions at the active sur aces of the anode andcathode, by maintaining intimate contact between the bath and the anodeand cathode, maintaining active circulation of the bath and anode, andcontrolling the composition of the bath and anode and the currentdensities at the active surfaces thereof.

15. In the refining comprising removing aluminum electrolytically from amolten alloy thereof as anode and depositing the aluminum on a moltenaluminum cathode through a suitable molten bath compounded to Huid at atemperature below that of material volatilization, said alloy beingcompounded to remain mobile at a temperature below that of materialvolatilzation of the bath, and giving free play to secondary reactionsat the active surfaces of the anode and cathode, b maintaining intimatecontact between t e bath and the anode and cathode, maintaining activecirculation of thebath and anode, and controlling the composition of thebath and anode and the current densities at the active surfaces thereof.a

v 16. In the refinin of aluminum, the steps comprisin the esta lishingin a suitable cell ath of fluoride containing aluminum iuorid,compounded to be fluid below the temperature of material volatilizationof aluminum luorid; a molten anode of aluminum alloy to be refined, comunded to rewithin a wor ing range of aluminum content, below thetemperature of material volatilization of the bath; and a of aluminum,the stepsmolten aluminum cathode; and passing electrolyzing current fromthe anode through the hath to the cathode in sutlicient quantity tomaintain said anode, cathode, and bath in mobile condition and transferaluminum from the anode to the cathode.

ll'. In the refining of aluminum` the steps comprising establishing in asuitable cell the gravitatively arranged -layersaamolten bath offluorids containing aluminum lluorid. com pounded to have a densityhigher than that of molten aluminum and to be fluid below thetemperature of material volatilization of aluminum fluorid, a moltenanode ol' aluminum allov to lie refined. compounded to have a densityhigher than that of said bath and to remain mobile, within a workingrange ot aluminum content, below the temperature of materialvolatilization of the bath; and a molten aluminum cathode: and passingelectrolyzing current from the anode through the bath to the cathode insufficient quantity to maintain said elements in mobile condition andtranst'er aluminum from the anode to the cathode.

18. In the refining of aluminum, the steps comprisingr removing aluminumelectrolytically from a molten aluminum-copper alloy ot low iron andtitanium content, as anode, containing silicon in such proportion to thecopper as to maintain adequate mobility ot the alloy during theelectrolysis; and depositing the aluminum so removed from a moltencathode.

l0. ln the refining of aluminum, the steps comprising removing aluminumelectrolyticall)Y from a molten aluminum-copper alloy ot' low iron andt'tanium content, as anode, containing silicon in such proportion to thecopper as to maintain adequate mobility of the alloy during theelectrolysis, with a suitable electrolyte and a current density lictween500 and 1.250 amperes, approximately, per square toot of cross sectionalarea of the eiectrolyte; and depositing thc aluminum so removed upon amolten aluminum cathode.

20. In the refining of aluminum, the steps comprising removing aluminumelectrolvtically Jfrom a molten anode alloy containing, approximately,30 per cent of aluminum, 55 per cent of copper, 10 per cent of silicon,less than 5 per cent of iron, and less than l per cent ot titanium, anddepositing the aluminum so removed on a molten aluminum cathode.

Q1. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten anode alloy contain ing. approximately,30 per cent of aluminum. 55 per cent of copper, 10 per cent of silicon.less than 5 per cent of iron, and less than l per cent of titanium, witha suitable electrolyte and a current density between 500 and 1250amparos. approximately, per square foot of cross sectional area of theelec- `about 10000 C. and

trolyte; and depositing the aluminum so removed upon a molten aluminumcathode.

22. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten aluminum alloy containing copper inamount not less than about 20 per cent, and silicon in amounts between 2and 32 per cent, approximately, of the copper-plus-silicon content, anddepositing the aluminum so removed on a molten aluminuln cathode.

In the refining of aluminum, the steps comprising removingr aluminumelectrolytically from a molten anode alloy of low iron and titaniumcontent containing aluminum about 30 per cent, copper about 55 per cent.and silicon about 10 per cent, and depositing the aluminum so removed ona molten aluminum cathode.

Q4. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten anode alloy of low iron and titaniumcontent containing aluminum, copper and silicon in proportions givingthe alloy suitable mobility 0500 C., and depositing the aluminum soremoved on a molten aluminum cathode.

25. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten alloy containing aluminum, copper, andsilicon, in proportions giving the alloy suitable mobility below about9500 C. and a density of not less than about 2.7 grams per cubiccentimeter at the temperature named, aluminum so removed on a moltenaluminum cathode.

20. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten aluminum-alloy containing copper andsilicon in proportions giving the alloy suitable mobility below about10000 C. when the aluminum content is reduced to the desired extent, anddepositing the aluminum so removed on a molten aluminum cathode.

27. In the refining of aluminum, the steps comprising removing aluminumelectrolytically from a molten aluminum-alloy containing silicon,copper, iron, and titanium, in proportions giving suitable mobilitybelow about 10000 C. when the aluminum content is reduced to the desiredextent, and depositing the aluminum so removed on a molten aluminumcathode.

28. In the refining of aluminum. the improvement comprising removingaluminum electrolytically from a molten aluminumalloy containing copper.silicon. iron, and titanium, in proportions giving the alloy, when thealuminum content is reduced to the desired extent. suitable mobilitybelow a density not less than about 2.7 grams per cubic centimeter atthe temperature mentioned, and depositing the below about and depositingthe lfltl llll lill

l lyte aluminum vso removed on num cathode. o

29. In the electrolytic refining of aluminum, the steps comprisingestablishing va lower layer of molten `aluminum-alloy as anodecontaining copper and a li hter ingredient in proportions giving the alo suitable mobility below 1100 C.and a ensity not less than'about 2.6grams per cubic centimeter at the temperature mentioned, an up r layerof molten aluminum as cathode, an an intermediate layer of moltenelectrolyte com d ofa mixture containin fluorids of a uminum and sodiumand tluorid of one or more alkali earth metals; and assing currentbetween the anode alloy an the aluminum cathode and through theelectrolyte; 'whereby' aluminum is removed from the anode ,and depositedon the cathode at a temperature below that mentioned.

30. In the electrolytic refining of aluminum., the steps comprisingestablishing a lower layer of molten aluminum-alloy as anode containingcopper and a lighter ingredient in proportions giving the alloy afreezing int below 1100 C. and a density not less t an about 2.6 gramsper cubic cen timeter at the temperature mentioned, an upper'layer ofmolten aluminum as cathode, and an intermediate layer of moltenelectrocompo'sed' of a mixture containing tluorids of aluminum andsodium and iluord of one or more alkali earth metals; and assiug currentbetween the anode alloy an the aluminum cathode and throughtheelectrolyte, with a current density between 500 and 1250 amperes,approximately, per square foot of cross sectional area of the electrolwhereby aluminum is removed from t ie anode and deposited on, thecathode at a temperature below that mentioned.

3l.V In the electrolytc rening of aluminum. the improvement comprisingestablishing in downwardly successive layers a body of molten aluminumas cathode, a body fof molten electrolyte composed of a mixturecontaining aluminum, sodium, and barium tluorids, and a lower body ofmolten aluminum-alloy as anode containing copper and silicon inproportions ivin a density higher than that of the e ectro yte mixtureand suitable mobilityl at a temperature not higher than about 1000 C?,and passing current through said layers in succession to remove aluminumfrom the lower layer and deposit it on the up r layer. t

-32. In the electro ytic refining of alumi-V num, the steps comprisingestablishing in downwardly successive la ers a body of molten aluminumas cat iode, a body of molten electrolyte comp of a mixture containingaluminum` sodium, and barium fluorids` and a body of molten alloy asanode containing aluminum about. 30 per cent,cop per about ."5 per rent,and silicon about 10 a molten alumiper cent; and passing currentthrough. said ayers in succession to remove aluminum from the lowerlayer 'und deposit it on the upper layer.

33. In the electrolytic refining of aluniinum, the steps comprisingestablishing in downwardly successive layers a body of molten aluminumas cathode, a body of molten electrolyte composed of a mixturecontaining aluminum, sodium, and barium fluoride, and a o mo lloyusanode containing aluminum about 30 er cent, copper about r cent; andpassing current through said ayers in succession witli a current densitybetween 500 and 1250 amperes, approxi mately, r square foot of crosssectional area of t e electrolyte, to remove aluminum from the lowerlayer and deposit it on the upper layer.

34. In the electrolytic refining of alumi- 55 per cent, and siliconabout 10 num, the steps comprising passing current through upwardlysuccessive molten layers composed respectively of a body of ahumnumalloy, as anode, containingcoppcr and a lighter metal in proportionsgiving a density at least as high as about 2.7 grams per cu icvcentimeter at a temperature of about 950 C.; a body ofelectrolytemixtiun containin aluminum, sodium, and barium uori s; and abody of molten aluminum as cathode; and by the passage of the currentkmaintaining the materials in the molten state and in the la erformation described while simultaneously removing aluminum fromV thelower layerand depositing it ou the upper layer; and maintaining thealumina content of the electrolyte-mixturo below the point ofsaturation.

'35. In the electrolytic refining of aluminum, the steps comprisingpassing current through upwardly successive molten layers composedrespectively of a body of aluminlim alloy, as anode` containing copperand a lighter metal in proportions giving a densit at least as high asabout 2.7 grams per cu ic centimeter at a temperature of aboutl 950 C.;a body of electrolyte-niixture routaining aluminum, sodium, and barium ffiuorids; and a body of molten aluminum asV cathode: with a currentdensity between 500 and 1250 ampei'es, approximately, per square foot ofcross sectional area of the electrolyte; and by the passage o'f the cur,

- rent maintaining the materials in the molten state and .in the layerformation described while simultaneously removing aluminum from thelower layer and depositin it on the 4upper layergand maintainin t ealumina content of the electrolyte-mixture below the point ofsaturation.

36. In the electrolytic refining of aluminum, the stepsiconiprisingestablishing a lower hiver of .molten aluminum alloy, as

anode, containing copper and `silicon in prollfl portions giving arelatively high density and adequate mobility when the aluminum coutentis relatively low, an upper layer of molten aluminum as cathode, and anintermediate layer of molten electrol te composed of a mixturecontaining a uminum, sodium and barium fluorids in proportions giving adensity between that o the anode alloy and that of the cathode aluminumwhen all are molten; establishing on the aluminum layer aheat-insulating top'crust composed, at least in part, of electrolytecoming up from below and freezing above the aluminum; passing currentthrough the successive layers to remove aluminum from the anode anddeposit it on the cathode; and treating the electrolyte to preventsaturation thereof with alumina and consequent thickening of the tocrust.

37. In the electro ytic reining of alumi num, the steps comprisingestablishing a lower layer of molten aluminum alloy, as anode,containing vcop r and silicon in proportions giving a relatively higlhdensity and adequate mobility when tie a uminum con- ,tent is relativelylow, an upper layer of molten aluminum as cathode, and an intermediatelayer of molten electrol te composed of a mixture containing a uminum,sodium and barium .iluorids in proportions giving a density between thatof the anode alloy and that of the cathode aluminum when all are molten;establishing on the aluminum layer a heat-insulating top-crust composed,at least in part, of electrolyte coming up from below and freezing abovethe aluminum; passing current with a density between 500 and 1250amperes, approximately, met square foot of cross sectional area of t eelectrolyte, through the successive layers to remove aluminum from theanode and deposit it on the cathode; and treating the electrolyte toprevent saturation thereof with alumina and consequent thickening of theto -crust.

3S. Tu the electro ytic refiningof aluminum, Ministeps comprisingestablishing a lower layer of molten alloy, as anode, -containingaluminum, cop r and silicon, on up er layer of molten a uminum ascathode, an an intermediate layer of molten electrolyte containingaluminum, sodium and barium fluoride; passing current through the layersin successionto remove aluminum from the lower and deposit it on theupper layer: and treatin the electrolyte at intervals to substantial ymaintain the same unsaturated with alumina and thereby prevent excessiverise of the freezing point of the electrolyte.

39. In the electrolytic refini of aluminum the ste comprising estalishing a 4lower ayer o molten aluminum alloy as anode containing copperand silicon in proportions giving a freezing point no higher than about1050 C., an upper layer of molten aluminum as cathode, and anintermediate layer of molten electrolyte containing aluminum, sodium andbarium iluorids; passing current through the said layers in successionto remove aluminum from the lower and deposit it on the upper iayer; anddeoxidizing the electrolyte as necessary to prevent rise of its freezingpoint above substantially the' temperature mentioned.

40. In the eleetrolytic refining of aluminum, the steps comprisingestablishing a lower layer of molten alloy, as anode, containingaluminum about 30 per cent, copper about 55 per cent, silicon about 10per cent, and containing less than about 5 per cent of iron and lessthan about 1 per cent of titanium; an upper layer of molten aluminum ascathode; and an intermediate layer of fluorid-electrolyte ofintermediate density; passing current through said layers in successionto remove aluminum from the anode and deposit it on the cathode; andfrom time to time deoxidizing the electrolyte to reduce alumina thereinand thereby prevent xceive rise of the freezing point of theelectrolyte.

41. In the electrolytic refining of aluminum, the ste comprisingestablishing a lower layer o molten alloy, as anode, con-t tainingaluminum about 30 per cent, copper about 55 per cent, silicon about 10percent, and containing less than about 5 per cent of iron and less thanabout 1 er cent of titanium; an upper layer of mo ten aluminum ascathode; and an intermediate layer of iluorid-electrolyte ofintermediate density; passing current through said `layers in successionto remove aluminum from the anode and deposit it on the cathode; fromtime to time deoxidizing the electrolyte to reduce alumina therein andthereby prevent excessive rise of the freezing point of the electrolyte;and maintaining the aluminum cathode layer sullicient in expanse toprevent excessive volatilization of the electrolyte.

42. An anode alloy of aluminum, containi suicient silicon to maintainadequate mo ilityl of the alloy as its aluminum content is dec inrening. 4

43. An anode-alloy containing aluminum, copper and silicon inproportions adapted to make the alloy adequately mobile below about 1050C.

44. An aluminum-copper anode-alloy containing silicon in amount at leastsufficient to keep the alloy ldequatel mobile at about 1050 C. whensubstantial y all the aluminum has been cted.

45. An aluminum anode-alloy containing copper and silicon in amountsadapted to. give the alloy a density not less than about 2.7 per cubiccentimeter at a temperatum of approximately 10009 46. An alrminnm ane-alloy containing copper not less than about 20 per cent, and siliconbetween Qand 32 per cent, approximately,- of the copper-plus-silicon.

47. An anode-alloy containing aluminum, copper and silicon inproporiafons adapted to make the alloy adequately "mobile below about105()o C., and having low iron and titanium content.

48. An aluminum anode-alloy containing copper and silicon in amountsadapted to give the alloy a. density not-less than about 2.7 grams percubic centimeter at a, temperature of approximately 1000 C.. and havingnot more than about 5 per cent of iron and titanium.

49. An aluminum anode-alloy containing copper not less than about 20 percent, and silicon between 2 and 32 per cent, ap toximately, of thecopper-plus-Silioon, an having not more than about 5 per cent of ironand titanium.

In testimony whereof We hereto aix our signatures.

' WILLIAM HOOPES.

FRANCIS C. FRARY. JUNIUS D. EDWARDS.

copper not less than about 20 per cent, and silicon between 2 and 32 percent, approxi mately; of tlie copper-plus-silicon.

47. An anode-alloy containing aluminum, copper and silicon inproportions adapted to make the alloy adequately 4mobile below about10500 C., and having low iron and titanium content.

48. An aluminum anode-alloy containing copper and silicon in amountsadapted to give the alloy a density not-less than about 2.7 grams percubic centimeter at a temperature ofV approximately 1000 C., and havinging not more than about 5 per cent of iron 90 and titanium.

In testimony whereof we hereto aix our signatures.

WILLIAM HOOPES. FRANCIS C. FRARY. JUN IUS D. EDWARDS.

v Certificate of Corretion. Y It is hereby certified that in LettersPatent No. 1,534,317, granted A' ril 21, 1925 u on the ap lication ofWilliam Hoopes, of Pittsburgh, and Francis unius D.

.Fi-ary dwards, of Oakmont, Pennsylvania, for an improvement inElectrolytic Production of Aluminum, an error appears in the printedspecification requiring correction as follows: Page 10, line 33, claim18, for the word from read upon; and that the said Letters Patent shouldbe 'read with this correction therein that the same may conform to therecord of the case in the Patent Oice.

Signed and sealed this'iSth day of August, A. D. 1925.

, [nml KARL FE'NNING, ,doti/ng Commissioner of Patents.

Certificate of Correction. l It is hereby certified that in LettersPatent No. 1,534,317, granted A' ril 21, 19253 :Jipon the aplication ofWilliam Hoopes, of Pittsburgh, and Francis Frary an unius D.

, dwards, of Oakmont, Pennsylvania., for an improvement in ElectrolyticProduction of Aluminum, an error appears in the printed specificationrequiring correction as follows: Page 10, line 33, claim 18, for theword from read upon; and that the seid Letters Patent should be readwith this correction therein that the same may conform to the record ofthe case in the Patent Oce.

Signed and sealed this18th day of August, A D. 1925.

A [nm] KARL FENNING,

' Acting Commissioner of Patents.

